This page in a nutshell: Using the rules in a manner contrary to their principles in order to "win" editing disputes is highly frowned upon by the Wikipedia community.

A Wikipedia editor engaging in Wikilawyering by using formal legal terms in an inappropriate way when discussing Wikipedia policy

Wikilawyering (and the related legal term pettifogging) is a pejorative term which describes various questionable ways of justifying Wikipedians' actions.
It may refer to certain quasi-legal practices, including:

In other words, a "wikilawyer" is a caricature drawn from a bad lawyer, and the term may also be used in other cases, e.g., when a person superficially judges other editors and their actions by jumping to conclusions and slapping labels while brandishing Wikipedia policies as a tool for defeating other Wikipedians rather than resolving a conflict or finding a mutually agreeable solution.

Wikipedia policies and procedures should be interpreted with common sense to achieve the purpose of the policy, or help with dispute resolution. Typically, wikilawyering raises procedural or evidentiary points in a manner analogous to that used in formal legal proceedings, often using ill-founded legal reasoning. It can serve to evade an issue or obstruct the crafting of a workable solution.

For example, while it is often impossible to definitely establish the actual user behind a set of sock puppets, it is not a defense that all the sockpuppets which emerge were not named in the request for arbitration.

As another example, the three-revert rule is intended to prevent edit-warring. An editor who reverts the same article three times day after day is violating the spirit, if not the letter, of the rule, and can thus be sanctioned for edit warring.

See here for an actual example of conflation of judicial proceedings and Wikipedia arbitration procedures. (It is probable the poster intended this to be satire in an attempt to make a point about a particular editing dispute.)

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Use of authentic legal skills by legal professionals or other persons trained and skilled in the arts of negotiation and advocacy is welcome in proceedings of the Arbitration Committee and on Wikipedia in a variety of contexts. Please see Wikipedia:Requests for arbitration/How to present a case for some suggestions regarding effective advocacy. Precis: common sense trumps process.

A common mistake of misguided advocacy is when editors appoint themselves mediators and proceed with judging the sides by telling others whether they are right or wrong, instead of helping the sides to better state their positions and to find common grounds. It is not uncommon that one side is indeed wrong, and in such a case a mediator begins to appear to take sides thus alienating the wrong side and triggering their defense instincts, further entrenching them against an amicable resolution.

Some Wikipedians allege that the charge of wikilawyering is used, particularly by Wikipedians more influential than them, to avoid giving careful attention to their claims. It is also said that newer users tend to believe nuanced complex policy (particularly WP:Neutral point of view) conforms to their own point of view, and will repeatedly refer to policy rather than providing rationale for their edits.

The word wikilawyering typically has negative connotations, much like the term meatpuppet; those utilizing the term should take care that it can be backed up and isn't frivolous (see WP:No personal attacks and WP:Civility).

In cases where it is possible a user is simply mistaken or naive and not deliberately deceiving others, efforts should be made to educate them rather than labeling their actions as "wikilawyering".

Like any pejorative, the term may easily result in fellow Wikipedians taking offense. At the same time, the notions of offense (in a debate) and insult should not be confused. While there is a blurred gray zone between offense and insult, the major distinction is that an offense in a debate is argumentative, while an insult is ... an insult, i.e., an act of demeaning an opponent. An offense is always specific, i.e., addresses a particular argument or reasoning, while an insult is generalizing and dismissive. For example, the phrase "You are wikilawyering" is an insult. On the other hand, the message "Therefore I conclude that you are stretching the WP:What Wikipedia is not policy here beyond common sense, i.e., you are wikilawyering", while aggressive, is not an insult, but rather a pointer to an identifiable wikibehavioral pattern. Similarly, "This proposal is wikilawyering a bit, because ..." is a comment on the content or nature of the proposal, not on the personality or motives of its author or supporters.

Because reasoned arguments in a debate necessarily include both elements of fact and references to principles, disputants who lack such an argument sometimes try to undermine arguments they can not otherwise overcome by just tossing out the naked accusation that their opponent is a wiki-lawyer. This is not a good faith tactic and does not foster a collegial consensus-seeking atmosphere. Therefore, any accusation of wikilawyering should include a brief explanation justifying use of the term.